WO2006095776A1

WO2006095776A1 - Semiconductor light modulator

Info

Publication number: WO2006095776A1
Application number: PCT/JP2006/304482
Authority: WO
Inventors: Ken Tsuzuki; Nobuhiro Kikuchi; Eiichi Yamada
Original assignee: Nippon Telegraph And Telephone Corporation
Priority date: 2005-03-08
Filing date: 2006-03-08
Publication date: 2006-09-14
Also published as: JP4933653B2; JPWO2006095776A1; JP2010271742A; EP1857857A4; CN101133355B; JP4663712B2; US7711214B2; US20090034904A1; CN101133355A; CN102033333A; EP2317371B1; EP1857857A1; CN102033333B; EP1857857B1; EP2317371A1

Abstract

There is provided a semiconductor light modulator capable of performing stable operation and having an excellent field resistance while exhibiting the characteristic of n-i-n structure semiconductor light modulator. The semiconductor light modulator includes a waveguide structure having an n-type InP clad layer (11), a semiconductor core layer (13) having the electro-optical effect, a p-InAlAs layer (15), and an n-type InP clad layer (16) which are successively overlaid. The electron affinity of the p-InAlAs layer (15) is smaller than the electron affinity of the n-type InP clad layer (16). In the waveguide structure having such a configuration, it is possible to arrange a non-dope InP clad layer (12) between the n-type InP clad layer (11) and the semiconductor core layer (13) and to arrange a non-dope InP clad layer (14) between the semiconductor core layer (13) and the p-InAlAs layer (15).

Description

Specification

Semiconductor optical modulator

Technical field

The present invention relates to a semiconductor optical modulator, and more particularly to a semiconductor optical modulator used in the fields of optical communication systems and optical information processing systems.

Background art

[0002] Due to the recent advancement of advanced information, it is desired to increase the capacity of information transmitted over networks such as the Internet. Optical communication systems and optical information processing systems have been proposed as communication systems capable of transmitting large amounts of information at high speed. Is attracting attention.

[0003] In recent optical communication systems and optical information processing systems, the large-capacity storage is progressing to meet the above demand. In such an optical communication system and an optical information processing system, in order to increase the transmission distance at high speed, it is affected by the dispersion of the fiber that causes the waveform deterioration, so that there is little wavelength checking. It is necessary to use an optical signal. Therefore, at present, the mainstream of optical signal generation is a combination of a DC-operated light source and an external modulator.

[0004] By the way, the waveguide type light control device is one of the key elements of a high-speed optical communication system and an optical information processing system. Among waveguide-type light control devices, an optical modulator is an indispensable device for converting electrical signals such as sound and images into light intensity. Optical modulators can be broadly divided into those using dielectrics such as LiNbO (LN), InP and GaAs.

Three

There are those using semiconductors.

[0005] As a typical external modulator (optical modulator), a dielectric such as LiNbO (LN) is used.

Three

LN modulator power that is widely used now. This operates using an electro-optic effect in which the refractive index of the medium is changed by applying an electric field having a frequency sufficiently lower than the direct current or optical frequency.

[0006] An optical modulator using such an electro-optic effect includes a phase modulator that modulates the phase of light by changing the refractive index of a dielectric having the electro-optic effect, and the phase modulator and Matsuhsanda. There is a light intensity modulator combined with an interference system. Matsuhatsu optical modulator Is a modulator suitable for ultra-high-speed long-distance transmission, which can theoretically reduce wavelength checking to zero.

However, since the conventional LN modulator has a relatively long element length, the optical transmitter module becomes large, and a high driving voltage of about 3 to 5 V is required. In addition, since the drive conditions change due to DC drift (DC voltage drift) and temperature drift, a separate control circuit was required for stable operation. That is, there is a problem that a drive condition control mechanism is required due to the change of the drive condition.

[0008] On the other hand, the following two optical modulators using semiconductors are typical. One is the long absorption edge by applying an electric field, such as the Franz-Keldysh effect in bulk semiconductors and the quantum confined stark effect (QCSE) in multiple quantum well structures. This is an electroabsorption optical modulator (EA modulator) that uses the effect of shifting toward the wavelength side. The other is an electro-optic modulator (EO modulator) that uses an electro-optic effect (Pockels effect) in which the refractive index changes when an electric field is applied.

[0009] An electroabsorption optical modulator (EA modulator) is a small LiNbO modulator that consumes less power

This is considered promising because there is no drift due to DC voltage as seen in Fig. 3. However, electroabsorption optical modulators (EA modulators) have a problem in that wavelength chasing occurs during modulation, and waveform degradation occurs after optical fiber transmission due to the chirping. In other words, the optical signal spectrum after modulation is broadened compared to that before modulation by wavelength checking. When an optical signal having a broad spectrum is transmitted through an optical fiber, waveform degradation occurs due to the dispersion effect of the optical fiber medium, which further adversely affects transmission characteristics. This phenomenon of waveform deterioration becomes more prominent as the bit rate is higher and the transmission distance is longer.

[0010] On the other hand, in an electro-optic modulator (EO modulator), a phase modulator that modulates the phase of light by changing the refractive index and a phase modulator are combined to form a Matsuhsunder interferometer. Matsuhsunder modulators for intensity modulation have been put into practical use. The current optical communication uses a Mach-Zehnder modulator that modulates the intensity because it sends the signal according to the intensity of the light. This Matsuhsunder modulator can theoretically reduce wavelength checking to zero, and is expected to be a very high-speed long-distance communication modulator. Semiconductor pine As an example of a Hazenda modulator, Non-Patent Document 1 discloses a lumped-constant type modulator having a pin structure. Since the optical modulator described in Non-Patent Document 1 has a pin structure, it is possible to efficiently apply an electric field to the core layer with a small leakage current.

[0011] Further, Non-Patent Document 2 discloses a modulator using a Schottky electrode. In the modulator described in Non-Patent Document 2, a wideband band is realized by using a traveling wave electrode structure as an electrode structure. Patent Document 1 also studies an n-i-n structure semiconductor Mach-Zehnder modulator aiming at lower voltage, smaller size, and higher speed.

[0012] Patent Document 1: International Publication No. 2004Z081638 Pamphlet

Non-Patent Document 1: C. Rolland et al., “10 Gbit / s, 1.56 μm multiquantum well InP / InGaAsP Mach-Zehnder optical modulator,” Electron, Lett., Vol.29, no.5, pp.471- 472, 1993 Patent Document 2: R. Spickerman et al., "GaAs / AlGaAs electro-optic modulator with ban dwidth> 40GHz," Electron, Lett., Vol.31, no.ll, pp.915-916, 1995

Disclosure of the invention

[0013] However, in the optical modulator described in Non-Patent Document 1, the resistance of the p-clad layer is high, so that the propagation loss of an electric signal is large and high-speed operation is difficult, and light absorption of the p-clad layer is also difficult. Due to the large size, it has been difficult to increase the element length in order to reduce the operating voltage. Further, the modulator described in Non-Patent Document 2 has a problem that the operating voltage is high.

[0014] Recently, a modulator having an n-i-n structure disclosed in Patent Document 1 described above has also been proposed. In the modulator described in Patent Document 1, an n−i−n structure is formed by sequentially stacking an n-type cladding layer, a core layer, and an n-type cladding layer, and an upper side that forms the n−i−n structure. The n-type cladding layer is provided with electrodes.

[0015] FIG. 11 is a cross-sectional view of a conventional phase modulation waveguide of an optical modulator having an optical waveguide having an nin structure. The substrate has a layer structure in which an n-type cladding layer 102, an optical waveguide core layer 103, a semi-insulating cladding layer 104, and an n-type cladding layer 105 are sequentially stacked. Electrodes 108 and 109 are connected to the n-type cladding layer 105 and the n-type cladding layer 102, respectively.

With such a configuration, a voltage is applied to the optical waveguide core layer 103 provided between the two n-type cladding layers 102 and 105 to operate. In this structure, p-i according to Non-Patent Document 1 As with the n structure, an electric field can be efficiently applied to the core layer, and since the n-type cladding layer is used, the electrical signal from the p cladding layer, which was a problem with the pin structure, and In addition, the propagation loss of light can be reduced, the operating voltage can be lowered, and a sufficiently stable output was obtained at that time. However, in recent years, with the further development of the optical communication system, further stability of the output of the optical modulator has been demanded.

[0017] However, the optical modulator having the phase modulation waveguide having the n-in structure such as Patent Document 1 has the following problems.

FIG. 12 is a diagram showing a waveguide band diagram of an optical modulator having an optical waveguide having an n-i-n structure. In the optical waveguide having the n-i-n structure, there is a light absorption in the optical waveguide core layer 103 although it is small. Therefore, as shown in FIG. 12, the holes 106-1 generated by light absorption become accumulated holes 106-2 in the semi-insulating clad layer 104 that is a noria layer. When these holes accumulate, the barrier of the semi-insulating clad layer 104 against electrons falls on the band diagram, and a leak current flows from the n-type clad layer 105 to the n-type clad layer 102 (parasitic phototransistor). Effect). In other words, in the case of transistor operation, when the base is open and the hole concentration of the base is increased, the same situation occurs as when the emitter Z base junction is forward biased.

Furthermore, due to the effect of the forward bias generated by the accumulated holes 106-2, the voltage applied to the optical waveguide core layer 103 is also reduced by a voltage corresponding to the forward bias. Therefore, there has been a problem that the modulation characteristics change depending on the wavelength and light intensity of light input to the optical modulator. For example, if the wavelength changes, it is necessary to change the driving conditions of the optical modulator, so a control circuit is required. Also, since the modulation characteristics fluctuate and deteriorate as the light intensity increases, it is necessary to limit the light input level. In order to avoid the fluctuation and instability of this modulation characteristic, there has been a restriction that an optical modulator must be used within a wavelength and light intensity range in which fluctuation does not become a problem. As a result, the range that can be used as an optical modulator has been limited.

[0020] As described above, the parasitic phototransistor effect caused by the accumulation of holes in the semi-insulating clad layer 104, which is a noria layer, has a phase modulation waveguide with a nin structure. This is a problem that hinders the stable operation of the optical modulator. One of the problems to be solved by the present invention is to suppress the hole accumulation and the parasitic phototransistor effect in the semi-insulating clad layer described above, and to suppress the fluctuation of the modulation characteristic caused by them, thereby controlling the modulator. It is to provide a structure that realizes the stable operation of the.

[0021] By the way, in order to apply an electric field to the core layer of the n-i-n structure, an electron potential barrier is required between the n-type cladding layer and the core layer to suppress electron leakage current. In the modulator described in Patent Document 1, in order to form this potential barrier, a Fe-doped semi-insulating layer is provided between the n-type cladding layer on which the electrode is formed and the core layer. . However, this structure has a frequency dispersion in the modulation intensity, which leads to an impediment to the stability of the output that is currently required!

[0022] Another problem to be solved by the present invention is to provide a semiconductor optical modulation that is capable of stable operation and has an excellent withstand voltage against electric field while taking advantage of the features of the nn-structure semiconductor optical modulator. Is to provide a vessel.

In order to achieve such an object, the first aspect of the present invention includes a first n-type semiconductor cladding layer, a semiconductor core layer, a semiconductor cladding layer, and a second n-type semiconductor cladding. And a waveguide structure formed by sequentially stacking layers, wherein the semiconductor clad layer has an electron affinity smaller than that of the second n-type semiconductor clad layer.

[0024] In the first aspect, the heterojunction between the semiconductor clad layer and the second n-type semiconductor clad layer may be of a type Π type.

[0025] In the first aspect, the potential energy for holes in the semiconductor clad layer may be smaller than the potential energy for holes in the semiconductor core layer.

[0026] In the first aspect, the potential energy for holes is smaller between the semiconductor cladding layer and the second n-type semiconductor cladding layer than the semiconductor cladding layer. 3 n-type semiconductor cladding layers may be inserted.

[0027] In the first aspect, a non-doped cladding layer may be inserted between the first n-type semiconductor cladding layer and the semiconductor core layer.

[0028] In the first aspect, the semiconductor core layer and the semiconductor clad layer In addition, a non-doped cladding layer may be inserted. The potential energy for holes in the semiconductor cladding layer may be smaller than the potential energy for holes in the non-doped cladding layer inserted between the semiconductor core layer and the semiconductor cladding layer.

[0029] In the first aspect, the semiconductor clad layer may be InAlAs.

[0030] In the first aspect, the semiconductor clad layer may be doped p-type.

[0031] In the first aspect, the waveguide structure may be a high-mesa waveguide structure or a ridge waveguide structure.

[0032] Further, in the first aspect, branching means for branching input light into two and outputting two output end forces, respectively, each of the two output ends being a separate waveguide. A branching means coupled to the input end of the structure and a multiplexing means coupled to the two waveguide structures respectively for combining and outputting the light output from the two waveguide structure forces. You may be prepared for.

[0033] In the first aspect, the first electrode formed in a region on the first n-type semiconductor clad layer, in which the semiconductor core layer is not formed, And a second electrode formed on the second semiconductor clad layer, and the first electrode and the second electrode may have a traveling wave electrode structure.

[0034] The second aspect of the present invention includes a first n-type semiconductor clad layer made of n-type InP, a first non-doped clad layer made of non-doped InP, a non-doped semiconductor core layer, and a non-doped InP. A semiconductor optical waveguide layer formed by sequentially laminating a second non-doped clad layer, a semiconductor clad layer comprising p-type InAlAs, and a second n-type semiconductor clad layer having n-type InP force. It is characterized by comprising a waveguide structure formed in this way.

[0035] A third aspect of the present invention includes a first n-type semiconductor clad layer made of n-type InP, a first non-doped clad layer made of non-doped InP, a non-doped semiconductor core layer, and a non-doped InP. A semiconductor optical waveguide layer formed by sequentially laminating a second non-doped clad layer, a semiconductor clad layer made of p-type InAlAs, a second n-type semiconductor clad layer having n-type InP force, and an n-type InGaAsP Or a third n-type semiconductor cladding layer of n-type InGaAlAs A waveguide structure formed by stacking is provided.

[0036] In a fourth aspect of the present invention, a first n-type semiconductor cladding layer, a semiconductor core layer, a semi-insulating semiconductor cladding layer, and a second n-type semiconductor cladding layer are sequentially stacked. A semiconductor optical modulator having a formed waveguide structure, which is a P-type semiconductor region that is a region having P-type conductivity, and has a certain length in the light traveling direction of the waveguide structure. At least one p-type semiconductor region formed on at least a part or all of the second n-type semiconductor cladding layer in the section, and formed on the P-type semiconductor region, and electrically connected to the P-type semiconductor region And a connected electrode.

[0037] In the fourth aspect, the p-type semiconductor region includes the second n-type semiconductor clad layer and the second n-type semiconductor clad having a certain length section in the light traveling direction of the waveguide structure. It may be formed on a part of the semiconductor cladding layer in contact with the pad layer.

[0038] Further, according to the fourth aspect, the electrode is formed on the p-type semiconductor region and the second n-type semiconductor clad layer, and the p-type semiconductor region and the n-type semiconductor layer are formed. The semiconductor clad layer may be electrically connected to the electrode in common.

[0039] Further, in the fourth aspect, the waveguide structure may be a high mesa waveguide structure or a ridge waveguide structure.

[0040] Further, in the fourth aspect, branching means for branching input light into two and outputting two output end forces, respectively, each of the two output ends being a separate waveguide. A branching means coupled to the input end of the structure and a multiplexing means coupled to the two waveguide structures respectively for combining and outputting the light output from the two waveguide structure forces. You may be prepared for.

[0041] Further, in the fourth aspect, the semiconductor device further includes a second electrode formed on a region on the first n-type semiconductor clad layer where the semiconductor core layer is not formed. In addition, the electrode may be formed on the p-type semiconductor region and the second n-type semiconductor clad layer, and the electrode and the second electrode may have a traveling wave electrode structure.

As described above, the semiconductor optical modulator according to the embodiment of the present invention can realize a semiconductor optical modulator that has low loss, excellent withstand voltage characteristics against an electric field, and operates stably at low voltage. That is, in one embodiment of the present invention, the electron affinity of the semiconductor cladding layer is Since it is set to be smaller than the electron affinity of the second n-type semiconductor clad layer, the semiconductor clad layer becomes a potential barrier against the electrons of the second n-type semiconductor clad layer. The frequency dispersion in intensity modulation is reduced or not generated.

[0043] According to one embodiment of the present invention, a part of the second n-type semiconductor clad layer in contact with the semiconductor clad layer (for example, a semi-insulating clad layer) or the second n-type semiconductor clad layer By forming a part of the semiconductor clad layer as a p-type semiconductor region having p-type conductivity, holes generated by light absorption are extracted from the electrode through the p-type semiconductor region. This prevents or reduces the accumulation of holes in the semiconductor cladding layer, which is a noria layer. For this reason, it is possible to suppress the occurrence of leakage current and the decrease in voltage applied to the semiconductor core layer, suppress the fluctuation of modulation characteristics due to light absorption, and realize stable operation of the modulator.

[0044] In a semiconductor electro-optic modulator (EO modulator) according to an embodiment of the present invention, holes are not accumulated or accumulated in a semiconductor cladding layer (eg, semi-insulating cladding layer) that is a barrier layer. Therefore, it is possible to suppress the occurrence of leakage current and the decrease in voltage applied to the core layer.

[0045] For this reason, it is possible to improve the conventional problem that the modulation characteristics of the optical modulator fluctuate depending on the light wavelength and light intensity, and to realize a stable operation of the modulator.

Brief Description of Drawings

[0046] FIG. 1 is a band diagram of a type II heterojunction according to one embodiment of the present invention.

FIG. 2 is a diagram showing a cross-sectional view of a waveguide structure according to an embodiment of the present invention.

FIG. 3 is a diagram showing a band diagram of a waveguide according to an embodiment of the present invention.

FIG. 4 is a diagram showing a voltage-current characteristic when an inverse noise is applied to the waveguide structure according to one embodiment of the present invention.

FIG. 5 is a diagram showing an EZE high frequency response characteristic when the length of the phase modulation region of the Mach-Zehnder modulator is 3 mm according to one embodiment of the present invention.

[Fig. 6] Fig. 6 shows a push-pull operation of a Mach-Zehnder modulator according to an embodiment of the present invention. It is a figure which shows the eye diagram of the made 40GbitZs.

FIG. 7 is a diagram showing a band diagram of a waveguide according to an embodiment of the present invention.

[Fig. 8] Fig. 8 is a schematic diagram of a Matsuhonda optical modulator according to an embodiment of the present invention.

FIG. 9 is a diagram showing a waveguide structure of an optical modulator according to an embodiment of the present invention.

[Fig. 10] Fig. 10 is a structural diagram of a Matsuhazu modulator according to an embodiment of the present invention.

[FIG. 11] FIG. 11 is a cross-sectional view of a waveguide of a conventional optical modulator having an nn structure.

[FIG. 12] FIG. 12 is a waveguide layer band diagram of a conventional optical modulator having an nn structure. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings described below, components having the same function are denoted by the same reference numerals, and repeated description thereof is omitted.

One embodiment of the present invention includes a first n-type semiconductor cladding layer, a semiconductor optical waveguide layer having an electro-optic effect formed on the first n-type semiconductor cladding layer, and formed on the semiconductor optical waveguide layer This is a semiconductor optical modulator having an n−n−n structure that also has a stacking force of the formed semiconductor clad layer and a second n-type semiconductor clad layer formed on the semiconductor clad layer. The semiconductor clad layer is a noria layer (potential barrier layer) for electrons having the second n-type semiconductor clad layer force.

[0048] In one embodiment of the present invention, it is important that the barrier layer functions well. In other words, it is important to reduce the effect of holes generated by light absorption in the semiconductor waveguide layer on the barrier layer.

[0049] The generated holes may be accumulated in the noria layer, and when accumulated in the noria layer, the potential barrier against electrons may be pushed down. Therefore, depending on the intensity of light incident on the semiconductor waveguide layer, the modulation characteristics change, frequency dispersion occurs in the intensity modulation, and the first n-type semiconductor layer force increases due to the potential barrier degradation. In some cases, a leakage current toward the semiconductor layer may occur. Therefore, the Hall force generated in the semiconductor waveguide layer. The effect on the barrier layer by accumulating in the S barrier layer. By reducing the above, it is possible to provide a semiconductor optical modulator capable of suppressing a variation in modulation characteristics and capable of stable operation.

[0050] In order to reduce the influence of the hole on the noria layer, in the first to third embodiments, even if it accumulates in the hole S barrier layer, it functions as a good noria for electrons. A conduction band discontinuity due to electron affinity occurs between the semiconductor clad layer as the barrier layer and the second n-type semiconductor clad layer. In the fourth and fifth embodiments, in order to reduce the influence of the hole on the noria layer, even if a hole generated by light absorption flows into the barrier layer, the potential barrier is maintained or the potential barrier is maintained. Try to reduce the rear drop.

[0051] (First embodiment)

In the semiconductor optical modulator according to the present embodiment, a first n-type semiconductor cladding layer, a semiconductor optical waveguide layer having an electro-optic effect, a semiconductor cladding layer, and a second n-type semiconductor cladding layer are sequentially stacked. Such a stacked body has an n-i-n structure. In this embodiment, the semiconductor cladding layer and the second n-type semiconductor cladding layer are heterojunction, and the electron affinity of the semiconductor cladding layer is Designed to be smaller than the electron affinity of the n-type semiconductor cladding layer. By doing so, the semiconductor cladding layer becomes a potential barrier against the electrons of the second n-type semiconductor cladding layer. As a result, the characteristics of semiconductor optical modulators with an n-i-n structure (reduction of light propagation loss, lower operating voltage, downsizing, high speed, etc.) are more stable and withstand voltage characteristics against electric fields. An excellent optical modulator can be realized.

[0052] Now, a type II heterojunction will be described. Figure 1 shows the band diagram for this type II heterojunction. q x (q: elementary electron) is called the electron affinity, and the bottom force of the conductor is the energy required to extract electrons into the vacuum. Eg is called the band gap and is the energy difference between the conductor and the valence band. Now, type II heterojunction means that the electron affinity of semiconductor 2 is smaller than that of semiconductor 1, and the sum of electron affinity and energy gap of semiconductor 2 (q% + Eg) and the force of semiconductor 1 Is also a small case. Here, considering the electrons in the conductor that flows from the semiconductor 1 side to the semiconductor 2 side, the conductor band discontinuity (A Ec = Ec -Ec)

twenty one

And only electrons with energy that can overcome this barrier will flow to semiconductor 2. Can not. In other words, for the electrons flowing from the semiconductor 1 side to the semiconductor 2 side, this bond is high resistance, and the greater the conductor band discontinuity, the greater the effect, and the better the breakdown voltage characteristic. It will be.

FIG. 2 is a cross-sectional view of the waveguide structure of the semiconductor optical modulator according to the present embodiment, and FIG. 3 is a view showing a band diagram of the waveguide structure shown in FIG.

In the semiconductor optical modulator according to the present embodiment, an n InP cladding layer (first n-type semiconductor cladding layer) 11, a semiconductor optical waveguide layer 19, p-InAlAs are formed on a semi-insulating (SI) -InP substrate 10. A layer (semiconductor cladding layer as a potential barrier layer) 15 and an n-InP cladding layer (second n-type semiconductor cladding layer) 16 are sequentially stacked. In the semiconductor optical waveguide layer 19, a non-doped InP clad layer 12, a non-doped semiconductor core layer 13 having an electro-optic effect, and a non-dope InP clad layer 14 are laminated, and p-InAlAs is formed on the InP clad layer 14. Layer 15 force S is to be stacked.

In this specification, “n-semiconductor” and “n-type semiconductor” refer to an n-type doped semiconductor. Of course, the same applies to p-type doping.

[0054] The semiconductor core layer 13 includes, for example, a multiple quantum well layer and a band gap larger than that of the multiple quantum well layer above and below (on the InP clad layer 12 side and InP clad layer 14 side of the semiconductor core layer 13). In addition, a structure having an optical confinement layer having a value smaller than that of the InP cladding layers 12 and 14 can be used. In addition, the band gap wavelength of the multiple quantum well layer is set so that the electro-optic effect is effective and the light absorption is not a problem at the light wavelength used.

Further, the waveguide structure according to the present embodiment has a high mesa waveguide structure as shown in FIG. 2 and applies a voltage to the semiconductor optical waveguide layer 19, so that the n-InP cladding layer 11 and Electrodes 17 and 18 are provided on the upper part of the n—InP clad layer 16, respectively.

In the present embodiment, a high mesa waveguide structure is used as the waveguide structure, but the present invention is not limited to this, and a ridge waveguide structure may be used.

Now, as can be understood from the band diagram when a voltage is applied to the semiconductor optical modulator according to the present embodiment shown in FIG. 3, the p-InAlAs layer 15 has more electrons than the n-InP cladding layer 16. Since the affinity is small, conduction band discontinuity occurs at the heterointerface between the two. That Therefore, a potential barrier against electrons in the n-InP cladding layer 16 is generated. In addition, since the p-In AlAs layer 15 is p-type and the n-InP clad layer 16 is n-type, a potential barrier due to a pn junction is generated in addition to a potential node caused by the heterojunction. Therefore, for the electrons injected from the n-InP clad layer 16, these two elements function as a total potential barrier.

In the present embodiment, as shown in FIG. 3, the heterojunction between the p-InAlAs layer 15 and the n-InP clad layer 16 is a type in which electrons and holes are confined in spatially different locations. It has become. In addition, the holes generated slightly due to light absorption in the semiconductor optical waveguide layer are easy to flow into the n-InP cladding layer 16 due to the non-doped InP cladding layer 14 side force. In the junction with the p-InAlAs layer 15, the potential energy for the holes of the p-In AlAs layer 15 is smaller than the potential energy for the holes of the non-doped InP cladding layer 14. In other words, at the junction between the semiconductor optical waveguide layer and the semiconductor clad layer as the potential barrier layer, it is preferable to reduce the potential energy for the holes of the semiconductor clad layer compared to the potential energy for the holes of the semiconductor optical waveguide layer. ,. When the cladding layer (in this embodiment, the non-doped InP cladding layer 14) is not provided between the semiconductor core layer and the semiconductor cladding layer, the layer in contact with the semiconductor cladding layer of the semiconductor optical waveguide layer is the semiconductor core layer. It becomes. In this case, the potential energy with respect to the holes in the semiconductor cladding layer should be made smaller than the potential energy with respect to the holes in the semiconductor core layer at the junction of the semiconductor core layer and the semiconductor cladding layer as the potential barrier layer.

Now, when the semiconductor optical modulator is operated, a slight force generates electrons and holes by light absorption in the semiconductor core layer 13, and these electrons easily reach the n-InP cladding layer 11. However, holes may accumulate near the p-InAlAs layer 15. This pushes down the potential NOR of the p-InAlAs layer 15. This corresponds to the reduction of the potential barrier due to the pn junction, which may prevent the breakdown voltage characteristics from being sufficiently maintained. However, in the structure according to this embodiment, the conduction band discontinuity remains the same even when the potential barrier due to the pn junction as described above is reduced. Since it can function as a potential barrier, it is possible to provide a semiconductor optical modulator with excellent breakdown voltage characteristics.

That is, even if holes generated in the semiconductor core layer 13 accumulate in the p-InAlAs layer 15 as a barrier layer, the potential barrier due to the pn junction is reduced. The electron affinity of the p-InAlAs layer 15 is expressed as n —The potential barrier due to the conduction band discontinuity generated by making the InP cladding layer 16 smaller than the electron affinity functions well. Therefore, the leakage current from the n-InP cladding layer 11 toward the n-InP cladding layer 16 can be reduced. In addition, the potential barrier due to the conduction band discontinuity works well regardless of the intensity and wavelength of the incident light on the semiconductor core layer 13, so the potential barrier due to the pn junction depends on the intensity and wavelength of the incident light. Even if it fluctuates, stable modulation can be performed.

Thus, in this embodiment, even if holes accumulate in the p-InAlAs layer (semiconductor clad layer) 15 that is a barrier layer, it is important to form a potential barrier without being affected by the accumulation of holes. It is. Therefore, in this embodiment, the electron affinity of the p-InAlAs layer 15 as the semiconductor cladding layer is made smaller than the electron affinity of the n-InP cladding layer 16 as the second n-type semiconductor cladding layer. is there.

By the way, what is concerned about making the p-InAlAs layer 15 p-type is light absorption caused by valence band interband transition. However, the conduction band discontinuity between the p-InAlAs layer 15 and the InP clad 14 is sufficiently large (the reference value is 0.39 eV), and it is not necessary to take much thickness. For example, if the p-InAlAs layer 15 has a thickness of 0.05 m, it can have a breakdown voltage of about 15V. In addition, since the magnitude of light absorption is proportional to the optical confinement factor of the p-layer, the p-InAlAs layer 15 is not made thicker than necessary, and the distance from the semiconductor core layer 13 is increased, that is, non-doped. It is possible to suppress loss due to light absorption by appropriately thickening the InP clad layer 14. As described above, in this embodiment, it is possible to realize a semiconductor optical modulator that has excellent breakdown voltage characteristics against an electric field without impairing the features of the semiconductor optical modulator having the nn structure, and that operates stably with low loss.

In this embodiment, the force using a stacked body of the InP clad layer 12, the semiconductor core layer 13, and the InP clad layer 14 as the semiconductor waveguide layer is not limited to this. That is, semiconductor A structure in which either one or both of the force InP cladding layers 12 and 14 are provided, in which the non-doped InP cladding layers 12 and 14 are provided above and below the core layer 13, respectively. In this embodiment, it suffices if light can be guided. As the semiconductor waveguide layer, either a semiconductor core layer alone or a non-dop cladding layer is provided on at least one of the upper and lower sides of the semiconductor core layer. Including. The non-doped InP cladding layers 12 and 14 have a wider band gap than the semiconductor core layer 13. For example, you can use InGaAsP or InAlGaAs layers.

[0063] Note that in the present embodiment, it is important to provide a potential barrier layer due to conduction band discontinuity between the semiconductor optical waveguide layer and the second n-type semiconductor cladding layer. Therefore, in this embodiment, the materials of the semiconductor cladding layer and the second n-type semiconductor cladding layer are not limited to p-InAlAs and n-InP, respectively, but the semiconductor cladding layer and the second n-type semiconductor cladding layer The materials of the semiconductor cladding layer and the second n-type semiconductor cladding layer are made so that the electron affinity of the semiconductor cladding layer is smaller than the electron affinity of the second n-type semiconductor cladding layer. Just choose. In addition, the semiconductor clad layer does not need to be p-type doped if a potential barrier layer due to conduction band discontinuity can be formed.

[0064] Considering that the voltage applied to the waveguide structure according to the present embodiment is a reverse bias, the semiconductor optical waveguide layer (InP clad layer 14 in FIG. 2) and the potential barrier layer are used. Although there is no particular limitation on the semiconductor clad layer, the electron affinity of the semiconductor clad layer is preferably smaller than the electron affinity of the semiconductor optical waveguide layer (InP clad layer 14 in FIG. 2).

A traveling wave electrode structure is useful for realizing a high-speed optical modulator. Therefore, traveling wave type electrodes may be applied to the electrodes 17 and 18. In this traveling-wave electrode structure, impedance matching in the optical modulator and speed matching between light and electricity are important. This impedance matching and velocity matching can be achieved by controlling the capacitance component of the optical waveguide of the optical modulator. In other words, it is important to appropriately design the total thickness and waveguide width of the semiconductor optical waveguide layer 19 (the semiconductor core 13 and the upper and lower non-doped InP cladding layers 12 and 14), which are non-doped layers. [0066] As specific impedance matching conditions, an error of about 50 Ω to ± 10 Ω, which is the specific impedance of the external electric circuit, can be allowed. In general, since the optical modulator is required to be driven at a low voltage, it is preferable to make the total thickness of the non-doped layer as thin as possible unless the optical confinement factor of the non-doped layer becomes extremely small (by doing this, Capacity increases). However, the characteristic impedance of the optical modulator is qualitatively inversely proportional to the square root of the capacitance, so if the non-doped layer is too thin, the characteristic impedance becomes too small. One way to avoid this is to reduce the width of the semiconductor optical waveguide layer. However, if it is too thin, this may lead to an increase in light propagation loss and a decrease in yield.

On the other hand, the frequency band depending on the degree of speed matching is expressed by the following equation.

[0068] [Equation 1]

Δ f _1.4 C / I n _{op E} -n ^ IL

[0069] where C is the speed of light, n is the group refractive index, n is the refractive index of electricity, and L is the electric power.

β

Extremely long.

[0070] The group index of refraction η of light is about 3.4 to 3.7, depending on the desired frequency band and electrode length.

opt

The allowable range of electrical refractive index is determined. For example, if the band is 40 GHz and the electrode length is 3 mm, the difference between the group refractive index of light and the refractive index of electricity is about ± 1.1. Qualitatively, when the capacitance of the semiconductor optical waveguide layer is increased, the speed of electricity is reduced, that is, the refractive index of electricity is increased. Considering that all of the above conditions are met, the optical waveguide width is 1.! It is preferable that the total thickness of the non-doped layer (semiconductor optical waveguide layer) is about 0.4 m to 2.0 μm.

[0071] (Example)

In the following examples, InP was used for the first and second n-type semiconductor clad layers. A p-type InAlAs layer (p — InAlAs layer 16) was used as the semiconductor cladding layer functioning as an electron potential barrier, and its layer thickness was 0.05 μm and the doping density was 1 × 10 ¹⁸ cm ³ . Further, the total thickness of the semiconductor optical waveguide layer 19, that is, the non-doped layer was set to 0.9 m. The width of the semiconductor optical waveguide layer 19 was 1.6 m.

[0072] Figures 4 to 6 show the characteristics of a Mach-Zehnder modulator fabricated using the above parameters. ing. FIG. 4 is a diagram showing voltage-current characteristics when a negative voltage is applied to the electrode 18 (reverse bias) between the electrode 17 and the electrode 18. As can be seen from Fig. 4, it shows a sufficient breakdown voltage characteristic of 15V or higher!

[0073] Fig. 5 shows the EZE high-frequency response characteristics in which the length of the phase modulation region is 3 mm.

From Fig. 5, it can be seen that the frequency of 6 dB down, which is the reference for the frequency band, is 40 GHz or more, and there is enough band for 40 GbitZs modulation.

[0074] Furthermore, Fig. 6 is a 40 GbitZs eye diagram that is actually push-pull operated at 1.3 Vpp. From Fig. 8, a clear eye opening can be confirmed. Thus, it can be seen that the Mach-Zehnder modulator according to this embodiment is useful as a high-speed optical modulator.

[0075] (Second Embodiment)

FIG. 7 is a diagram showing a band diagram of the waveguide structure of the semiconductor optical modulator according to the present embodiment.

The basic configuration of the semiconductor optical modulator according to this embodiment is the same as that of the first embodiment, and the description thereof is omitted. The difference between this embodiment and the first embodiment is that the second n-type semiconductor cladding layer n-InP cladding layer 16 and the potential noria layer p-InAlAs layer 15 Compared to the n-InP clad layer 16 which is an n-type semiconductor clad layer, the potential energy for holes is small! / and the third n-type semiconductor clad layer 20 is inserted. The third n-type semiconductor clad layer 20 can be formed by appropriately setting the composition of, for example, an InGaAsP layer or an InGaAlAs layer.

[0076] Thereby, holes generated by slight optical absorption in the semiconductor core layer 13 during operation fall into the second n-type semiconductor cladding layer 20 without being accumulated in the p-InAlAs layer 15. . The fallen holes can quickly recombine with the electrons in the third n-type semiconductor clad layer 20, so that the potential barrier can be prevented from lowering due to the accumulation of holes. That is, with this configuration, it is possible to provide a semiconductor optical modulator that is more excellent in breakdown voltage characteristics against an electric field and operates stably.

[0077] (Third embodiment)

In the present embodiment, a Mach-Zehnder optical modulator using the waveguide structure (phase modulation waveguide) described in the first and second embodiments will be described. According to this embodiment The Matsuhazu optical modulator 40 has the waveguide structure described in the first and second embodiments.

[0078] In Fig. 8, two output ends of an MMI (Multi-Mode Interferencé) force bra 42a as means for branching the input light into two are respectively provided in the phase modulation waveguide according to the embodiment of the present invention. 41a and 41b are linked. The output ends of the phase modulation waveguides 41a and 41b are respectively connected to the two input ends of the MMI coupler 42b as means for multiplexing the two input lights. Further, an electrode 43 is provided in a predetermined region of the first n-type semiconductor clad layer formed on the substrate, and an electrode 44 is provided in a predetermined region on the phase modulation waveguides 41a and 41b. In this embodiment, the length L (phase modulation region) of the phase modulation waveguides 41a and 41b is 3 mm.

In such a configuration, when input light is input from one input end of the MMI coupler 42a, the input light is branched into two by the MMI coupler 42a, and each of the branched lights is phase-modulated. Guided to waveguides 4 la and 4 lb. At this time, the phase of the branched light that passes through the phase modulation waveguides 41a and 41b is modulated based on the voltage applied to the phase modulation regions of the phase modulation waveguides 41a and 41b by the electrodes 43 and 44. The modulated light is multiplexed by the MMI force coupler 42b and output from one output terminal of the MMI coupler 42b.

[0080] According to the present embodiment, it is possible to provide a Mach-Zehnder type optical modulator that has excellent breakdown voltage characteristics against an electric field without impairing the features of the semiconductor optical modulator having the n-in structure and operates stably.

[0081] (Fourth embodiment)

The optical modulation waveguide used in the optical modulator according to this embodiment is a part of the second n-type semiconductor clad layer in contact with the semi-insulating clad layer as the semiconductor clad layer (barrier layer), or the second Part of the n-type semiconductor clad layer and the semi-insulating clad layer (semiconductor clad layer) is a p-type semiconductor region with p-type conductivity. A plurality of p-type semiconductor regions are repeatedly arranged in the light traveling direction of the light modulation waveguide. Holes generated by light absorption of input light in the semiconductor optical waveguide layer are extracted from the electrode common to the second n-type semiconductor clad layer through this p-type semiconductor region. Thereby, it is possible to prevent or reduce the accumulation of holes in the semi-insulating clad layer which is the NOR layer. Hall accumulation doesn't happen As a result, the accumulation of holes or the accumulation of holes can be reduced, so that it is possible to suppress the occurrence of leakage current and the decrease in the voltage applied to the optical wave core layer.

Therefore, one of the objects of the present invention is to improve the problem that the modulation characteristics fluctuate depending on the wavelength and intensity of light input to the optical modulator, and realize stable operation of the modulator. It becomes possible to do.

FIG. 9 shows the structure of the waveguide of the semiconductor optical modulator configured according to this embodiment.

On a semi-insulating InP substrate 51, an n— InP cladding layer 52 (first n-type semiconductor cladding layer), a semiconductor core layer 53, a semi-insulating cladding layer (semiconductor cladding layer as a potential barrier layer) 54 and n— InP cladding layer (second n-type semiconductor cladding layer) 55-1 has a layered structure. In the optical modulation waveguide part, n-InP cladding layer 55-1 and a part of semi-insulating cladding layer 54 in contact with the semi-insulating cladding layer 54 in a section of a certain length in the light traveling direction are p-type. These are called P-type semiconductor regions 55-2a to 55-2d with the conductivity of. An electrode 56 electrically connected in common with the p-type semiconductor regions 5552a to 55-2d and the n-InP cladding layer 55-1 is provided. This p-type semiconductor region is repeatedly arranged in the light traveling direction over the entire light modulation waveguide. In FIG. 9, they are repeatedly arranged at regular intervals, but are not limited to regular intervals. That is, they may be arranged at random intervals. In FIG. 9, the number of p-type semiconductor regions is not limited to only four forces, which are described, but a large number of p-type semiconductor regions are repeatedly arranged over the entire optical modulation waveguide.

[0085] The p-type semiconductor regions 55-2a to 55-2d are formed, for example, after the layers from the n-InP cladding layer 52 to the n-InP cladding layer 55-1 are grown, and then the p-type semiconductor region 55- 2a ~ 55— The part corresponding to 2d is removed by etching! / And then, it can be formed by re-growing the p-type InP semiconductor region. It can also be formed by introducing a Be acceptor into a part of the n—InP clad layer 55-1 by ion implantation. However, it is desirable that the p-type semiconductor regions 55-2a to 55-2d do not penetrate into the semiconductor core layer 53. The length of the p-type semiconductor region in the light traveling direction can be set to 50 m or less, for example. Also p-type half The interval between the conductor regions can be set to 200 m or less, for example.

[0086] On the n-InP cladding layer 55-1 and the n-InP cladding layer 52, an electrode 56 and electrodes 57a and 57b, which are metal electrodes, are arranged, respectively. A voltage is applied to the semiconductor core layer 53 with the electrode 56 having a negative polarity with respect to the electrodes 57a and 57b. The electrode 56 makes a common electrical contact with both the n—InP cladding layer 55-1 and the p-type semiconductor regions 55-2a to 55-2d.

In this embodiment, in order to reduce the influence of holes generated by light absorption in the semiconductor core layer 53 on the semi-insulating clad layer 54 that is a barrier layer, the above-described Hall force ¾ type semiconductor region is used. It flows into the electrode 56 through 55-2a to 55-2d. As described above, since the holes flow into the electrode 56, holes are not accumulated in the semi-insulating clad layer 54, or accumulation can be reduced. Accordingly, accumulation in the semi-insulating clad layer 54 can be prevented or reduced, so that the potential barrier of the semi-insulating clad layer 54 can be maintained, or reduction in potential barrier can be reduced. You can.

In the present embodiment, the electrode 56 functions as a means for sucking holes in addition to functioning as a means for applying an electric signal by applying a voltage to the semiconductor core layer. At this time, in order for the electrode 56 to function so as to absorb the holes, a path through which the holes pass between the semi-insulating clad layer 54 and the electrode 56 is necessary, and the p-type semiconductor region 55-2a to 55 — 2d serves as the path. That is, the holes in the semi-insulating clad layer 54 move to the outside of the semi-insulating clad layer 54 by the electrode 56 and the p-type semiconductor regions 55-2a to 55-2d. The influence on the semiconductor clad layer (semi-insulated clad layer 54) as a layer can be reduced.

[0089] Note that the p-type semiconductor region is directed from the semi-insulating clad layer 54 to the electrode 56.

In order to function as a (path for extracting holes from the semi-insulating clad layer 54), it is preferable that the P-type semiconductor regions 55-2a to 55-2d and the electrode 56 are brought into contact with each other. In FIG. 9, the p-type semiconductor regions 55-2a to 55-2d are also formed in part of the semi-insulating clad layer 54, but this is not restrictive. That is, in this embodiment, it is important to flow holes in the semi-insulating clad layer 54 to the electrode 56, and the p-type semiconductor regions 55-2a to 55-2d function as the above-described hole paths. That is important. Therefore, semi-insulated type The p-type semiconductor region may be formed in contact with the semi-insulating clad layer 54 without forming the p-type semiconductor region up to a part of the ladder layer 54. In addition, the p-type semiconductor region 55-2a to 55-2d may not be in contact with the semi-insulating clad layer 54 as long as the p-type semiconductor region 55-2a to 55-2d functions appropriately as the above-described hole path.

In this embodiment, an electrode for applying an electric signal and an electrode for sucking and taking holes are made common. In other words, the force that the electrode 56 has a function for applying an electric signal and a function for sucking out holes. Thus, by making the electrodes common, the apparatus can be simplified and the manufacturing process can be simplified. This is preferable because it can be simplified. However, the present invention is not limited to this, and an electrode for applying an electrical signal and an electrode for absorbing holes may be provided separately. For example, an electrode for absorbing and removing holes may be provided on the side surface of the n-InP clad layer 55-1 where the electrode 56 is formed.

[0091] Using the optical waveguide having the structure described above as an optical modulation waveguide, the optical modulator is operated as described below. Light is incident in a direction perpendicular to the cross section (end face) of the mesa structure shown in Fig. 9, and the light is propagated through the light modulation waveguide. In this state, an electric signal is input to the electrode 56, and an electric signal voltage is applied between the n—InP cladding layer 52 and the n—InP cladding layer 55-1. Fe atoms doped in the semi-insulating clad layer 54 act as acceptors at deep levels. For this reason, as explained in Fig. 12, it raises the energy of the valence band and acts as a potential barrier against electrons. This potential barrier suppresses electron injection from the n-InP cladding layer 55-1. Therefore, it is possible to modulate the optical phase based on the electro-optical effect by applying the electric signal voltage to the semiconductor core layer 53 in a state where the leakage current flowing from the electrodes 57a and 57b is small.

Next, the operation of the p-type semiconductor regions 55-2a to 55-2d showing effects peculiar to the present embodiment will be described. The p-type semiconductor regions 5 5-2 a to 55-2 d electrically connected in common with the n-InP cladding layer 55-1 have the following operations. In other words, in the conventional light modulation waveguide structure, as described in FIG. 12, the parasitic phototransistor effect occurs due to the holes accumulated by the light absorption of the semiconductor core layer 53. However, the p-type semiconductor region 55-2a to 55-2d, which is a characteristic part of this embodiment, is a noria layer. Holes flow from the semi-insulating clad layer 54 into the p-type semiconductor regions 55-2a to 55-2d, and accumulation of holes in the semi-insulating clad layer 54, which is a noria layer, can be suppressed. Therefore, the parasitic phototransistor effect described above is suppressed, and fluctuations in the modulation characteristics of the optical modulator can be suppressed.

In the present embodiment, a plurality of p-type semiconductor regions are arranged. However, the present invention is not limited to this, and only one p-type semiconductor region may be arranged. In this embodiment, it is important to establish a path for holes to flow to the insulating clad layer (semiconductor clad layer) force electrode. If the above path can be established, the number of p-type semiconductor regions is essential. It is not. In other words, in this embodiment, it is sufficient to arrange at least one p-type semiconductor region.

[0094] However, when a plurality of p-type semiconductor regions are arranged as shown in FIG. 9, the p-type semiconductor regions 55-2a to 55-2d are formed in the n-InP cladding layer 55-1. As for the region, the hole in a region far away from a certain P-type semiconductor region force is sucked up by the P-type semiconductor region force next to the certain P-type semiconductor region, so that the entire optical modulation waveguide section is covered. Therefore, the hall can be sucked up evenly. Therefore, it is preferable to arrange a plurality of p-type semiconductor regions.

[0095] (Fifth embodiment)

FIG. 10 is an overview of the semiconductor Mach-Zehnder modulator according to this embodiment. Matsuno and Tunda modulators have two n-i-n optical waveguides. Some of the two optical waveguides include phase modulation waveguides 62a and 62b, respectively, and the semiconductor optical modulation paths having the structure shown in FIG. 9 are used for the phase modulation waveguides 62a and 62b. . The phase modulation waveguides 62a and 62b are connected to optical multiplexers / demultiplexers 65a and 65b at two locations, respectively. The optical multiplexer / demultiplexer 65 a is further connected to the input waveguide 61, and the other optical multiplexer / demultiplexer 65 b is further connected to the output waveguide 63. Input light is input to the input waveguide 61, and output light is output from the output waveguide 63 force.

[0096] The Mach-Zehnder interferometer configured as described above enables light intensity modulation.

That is, the input light that has entered even one force of the input waveguide 61 is divided into two phase modulation waveguides 62a and 62b by the optical multiplexer / demultiplexer 65a. Each phase modulation waveguide 62a, 6 After performing phase modulation in 2b, it is again synthesized by the optical multiplexer / demultiplexer 65b. The phase of the optical signal in the waveguide is modulated by changing the refractive index of the phase modulation waveguides 62a and 62b by the electric signal that also receives the coplanar waveguide force. The signal lights that have undergone phase modulation in the phase modulation waveguides 62a and 62b are interfered and synthesized by the optical multiplexer / demultiplexer 65b, and output as one output intensity-modulated output light in the output waveguide 63. In order to perform optical modulation at high speed, a structure of a coplanar waveguide 64 is adopted for an electrode to which a high-frequency electric field as a modulation signal is applied.

The phase modulation waveguides 62a and 62b described above use the n-in structure light modulation waveguide having the P-type semiconductor region characteristic of the present invention described in the fourth embodiment. In the semiconductor phase modulation waveguides 62a and 62b according to the present embodiment, holes are not accumulated or accumulated in the semi-insulating clad layer, which is a noria layer, by providing a P-type semiconductor region in a part of the optical waveguide. It is reduced. Therefore, the parasitic phototransistor effect does not occur or can be suppressed, and it is possible to suppress the generation of leakage current and the voltage drop across the optical waveguide core layer. As a result, it is possible to improve the problem that the modulation characteristics fluctuate depending on the wavelength and intensity of light input to the optical modulator, and to realize a stable operation of the modulator.

Claims

The scope of the claims

[I] comprises a waveguide structure formed by sequentially laminating a first n-type semiconductor clad layer, a semiconductor core layer, a semiconductor clad layer, and a second n-type semiconductor clad layer,

A semiconductor optical modulator, wherein an electron affinity of the semiconductor clad layer is smaller than an electron affinity of the second n-type semiconductor clad layer.

2. The semiconductor optical modulator according to claim 1, wherein a heterojunction between the semiconductor clad layer and the second n-type semiconductor clad layer is a type II type.

3. The semiconductor optical modulator according to claim 1, wherein the potential energy with respect to holes in the semiconductor clad layer is smaller than the potential energy with respect to holes in the semiconductor core layer.

[4] Between the semiconductor clad layer and the second n-type semiconductor clad layer, the potential energy for holes is smaller than that of the semiconductor clad layer, and the third n-type semiconductor clad layer 2. The semiconductor optical modulator according to claim 1, wherein the semiconductor optical modulator is inserted.

5. The semiconductor optical modulator according to claim 1, wherein a non-doped cladding layer is inserted between the first n-type semiconductor cladding layer and the semiconductor core layer.

6. The semiconductor optical modulator according to claim 1, wherein a non-doped cladding layer is inserted between the semiconductor core layer and the semiconductor cladding layer.

7. The semiconductor optical modulator according to claim 6, wherein the potential energy for holes in the semiconductor clad layer is smaller than the potential energy for holes in the non-doped clad layer.

8. The semiconductor optical modulation according to claim 1, wherein the semiconductor clad layer is InAlAs.

9. The semiconductor optical modulator according to claim 1, wherein the semiconductor clad layer is doped p-type.

10. The semiconductor optical modulator according to claim 1, wherein the waveguide structure is a high mesa waveguide structure or a ridge waveguide structure.

[II] A branching means for splitting the input light into two and outputting the two output end forces, respectively. The two output ends are connected to the input ends of the separate waveguide structures, respectively. And

Coupling means coupled to the two waveguide structures, respectively, for combining the two waveguide structure forces and outputting the output light;

The semiconductor optical modulator according to claim 1, further comprising:

[12] A region on the first n-type semiconductor clad layer, the first electrode formed on the region, the semiconductor core layer being formed, and

The second electrode formed on the second semiconductor clad layer, wherein the first electrode and the second electrode have a traveling wave type electrode structure. Semiconductor light modulator.

[13] a first n-type semiconductor cladding layer made of n-type InP, a first non-doped cladding layer made of non-doped InP, a non-doped semiconductor core layer, and a second non-doped cladding layer made of non-doped InP Waveguide structure formed by sequentially laminating a semiconductor optical waveguide layer formed by sequentially laminating semiconductor layers, a semiconductor clad layer composed of p-type InAlAs, and a second n-type semiconductor clad layer composed of n-type InP A semiconductor optical modulator comprising:

[14] a first n-type semiconductor cladding layer made of n-type InP, a first non-doped cladding layer made of non-doped InP, a non-doped semiconductor core layer, and a second non-doped cladding layer made of non-doped InP A semiconductor optical waveguide layer formed by sequentially stacking, a semiconductor clad layer made of p-type InAlAs, a second n-type semiconductor clad layer made of n-type InP, and an n-type InGaAsP or n-type InGaAlAs A semiconductor optical modulator comprising a waveguide structure formed by sequentially laminating a third n-type semiconductor clad layer.

[15] A waveguide structure formed by sequentially laminating a first n-type semiconductor clad layer, a semiconductor core layer, a semi-insulating semiconductor clad layer, and a second n-type semiconductor clad layer A semiconductor optical modulator,

A p-type semiconductor region, which is a region having p-type conductivity, and is formed in at least a part or all of the second n-type semiconductor cladding layer in a certain length section in the light traveling direction of the waveguide structure. And at least one p-type semiconductor region,

An electrode formed on the P-type semiconductor region and electrically connected to the p-type semiconductor region; A semiconductor optical modulator comprising:

[16] The p-type semiconductor region is in contact with the second n-type semiconductor cladding layer and the second n-type semiconductor cladding layer in a certain length section in the light traveling direction of the waveguide structure. 16. The semiconductor optical modulation according to claim 15, wherein the semiconductor optical modulation is formed in a part of the cladding layer.

[17] The electrode is formed on the p-type semiconductor region and the second n-type semiconductor clad layer, and the p-type semiconductor region and the n-type semiconductor clad layer are electrically connected to the electrode. 16. The semiconductor optical modulator according to claim 15, wherein the optical modulators are connected to each other.

18. The semiconductor optical modulator according to claim 15, wherein the waveguide structure is a high mesa waveguide structure or a ridge waveguide structure.

[19] Branch means for branching the input light into two and outputting the two output end forces, respectively. The two output ends are connected to the input ends of the separate waveguide structures, respectively. And

16. The semiconductor optical modulator according to claim 15, further comprising:

[20] The method further comprises a second electrode formed on a region on the first n-type semiconductor clad layer where the semiconductor core layer is not formed,

The electrode is formed on the p-type semiconductor region and the second n-type semiconductor cladding layer,

16. The semiconductor optical modulator according to claim 15, wherein the electrode and the second electrode have a traveling wave type electrode structure.